Improvement in respect of shape (6)
I believe the answer is:
reform
'improvement' is the definition.
(I know that reform is a type of improvement)
'respect of shape' is the wordplay.
'respect of' becomes 're' ('re' means regarding or about).
'shape' becomes 'form' (synonyms).
're'+'form'='REFORM'
'in' is the link.
(Other definitions for reform that I've seen before include "Change one's ways (for the better?)" , "Go straight" , "Removal of abuses" , "Mend one's ways" , "Show improvement" .)